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What Caused The Ordovician Radiation (Biodiversity "Explosion")?

ramonmercado

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Study Bolsters Greenhouse Effect Theory, Solves Ice Age Mystery

COLUMBUS, Ohio – Critics who dismiss the importance of greenhouse gases as a cause of climate change lost one piece of ammunition this week. In a new study, scientists found further evidence of the role that greenhouse gases have played in Earth’s climate.


In Thursday’s issue of the journal Geology, Ohio State University scientists report that a long-ago ice age occurred 10 million years earlier than once thought. The new date clears up an inconsistency that has dogged climate change research for years.

Of three ice ages that occurred in the last half-billion years, the earliest ice age posed problems for scientists, explained Matthew Saltzman, assistant professor of geological sciences at Ohio State.

Previous studies suggested that this particular ice age happened during a time that should have been very warm, when volcanoes all over the earth’s surface were spewing carbon dioxide (CO2) and other heat-trapping greenhouse gases into the atmosphere.

With CO2 levels as much as 20 times higher than today, the late Ordovician period (460-440 million years ago) wasn’t a good time for growing ice.

Critics have pointed to the inconsistency as a flaw in scientists’ theories of climate change. Scientists have argued that today’s global climate change has been caused in part by buildup of CO2 in the atmosphere resulting from fossil fuel emissions.

But, critics have countered, if CO2 truly raises global temperatures, how could an ice age have occurred when a greenhouse effect much greater than today’s was in full swing?

The answer: This particular ice age didn’t begin when CO2 was at its peak -- it began 10 million years earlier, when CO2 levels were at a low.

“Our results are consistent with the notion that CO2 concentrations drive climate.”

Saltzman and doctoral student Seth Young found that large deposits of quartz sand in Nevada and two sites in Europe -- Norway and Estonia -- formed around the same time, 440 million years ago. The scientists suspect that the sand formed when water levels fell low enough to expose quartz rock, so that wind and rain could weather the rock into sand.

The fact that the deposits were found in three different sites suggests that sea levels may have been low all over the world at that time, likely because much of the planet’s water was bound in ice at the poles, Saltzman said.

Next, the scientists examined limestone sediments from the sites and determined that there was a relatively large amount of organic carbon buried in the oceans -- and, by extension, relatively little CO2 in the atmosphere -- at the same time.

Taken together, the evidence suggests that the ice began to build up some 10 million years earlier than when volcanoes began pumping the atmosphere full of the CO2 that ended the Ordovician ice age.

For Saltzman, the find solves a long-standing mystery.

Though scientists know with a great degree of certainty that atmospheric CO2 levels drive climate change, there are certain mismatches in the geologic record, such as the Ordovician ice age -- originally thought to have begun 443 million years ago -- that seem to counter that view.

“How can you have ice when CO2 levels are through the roof? That was the dilemma that we were faced with. I think that now we have good evidence that resolves this mismatch,” Saltzman said.

Scientists at the three sites previously attributed these quartz deposits to local tectonic shifts. But the new study shows that the conditions that allowed the quartz sand to form were not local.

“If sea level is dropping globally at the same time, it can’t be a local tectonic feature,” Saltzman said. “It’s got to be the result of a global ice buildup.”

Saltzman wants to bolster these new results by examining sites in Russia -- where he hopes to find more evidence of sea level drop -- and in parts of South America and North Africa, which would have been covered in ice at the time.

http://www.sciencedaily.com/releases/20 ... 223438.htm

Editor's Note: The original news release can be found here.
http://researchnews.osu.edu/archive/earlyice.htm
 
Here's an alternate explanation for what caused the Great Ordovician Biodiversification Event (GOBE) - a major asteroid collision.
One of Earth's Biggest Explosions of Life May Have Been Triggered by Asteroid Dust

Something mysterious happened nearly half a billion years ago that triggered one of the most important changes in the history of life on Earth. Suddenly, there was an explosion of species, with the biodiversity of invertebrate animals increasing from a very low level to something similar to what we see today.

The most popular explanation for this "Great Ordovician Biodiversification Event" is that it was a result of an uncomfortably hot Earth cooling and eventually heading into an ice age.

But what actually triggered the change in temperature? In our new paper, published in Science Advances, we show that its onset coincided exactly with the largest documented asteroid breakup in the asteroid belt during the past two billion years, caused by a collision with another asteroid or a comet.

Even today, almost a third of all meteorites falling on Earth originate from the breakup of this 150 kilometre-wide asteroid between Jupiter and Mars.

Following this event, enormous amounts of dust would have spread through the solar system. The blocking effect of this dust could have partly stopped sunlight from reaching the Earth – leading to cooler temperatures. We know that this involved the climate changing from being more or less homogeneous to becoming divided into climate zones – from Arctic conditions at the poles to tropical conditions at the equator.

The high diversity among invertebrates, including green algae, primitive fish, cephalopods and corals, came as an adaptation to the new climate.

Swedish sea floor

Our evidence comes from detailed studies of sea floor sediments of Ordovician age (485m-443m years ago) exposed at Kinnekulle in southern Sweden and Lynna River near St. Petersburg in Russia.

In a quarry at Kinnekulle, we found more than 130 "fossil meteorites" – rocks that fell on Earth in the ancient past, which became embedded in sea floor sediments and were preserved just like animal fossils.

All but one of these fossil meteorites, which are up to 20cm in diameter, have the same composition – they are all debris from the same collision. Indeed, they were made up of the same type of material as the large asteroid that broke up in the asteroid belt at the time.

The other meteorite probably originates from the smaller body that hit the large asteroid.

We know that the asteroid collision took place 466m years ago. This can be dated by looking at isotopes (variants of chemical elements with a different number of neutrons in the nucleus) in recently fallen meteorites from the Ordovician asteroid breakup.

The fossil meteorites in the quarry must therefore represent the material that was transported to Earth immediately after the breakup. And given the large number of meteorites that we found on the sea floor, we can estimate that the flux of meteorites to Earth must have been orders of magnitude higher back then than it is today.

But how do we know that this bombardment created a huge amount of dust that lowered the temperature? We also studied the distribution of very fine-grained, micrometre-sized dust in the sedimentary strata.

We could determine that it had an extraterrestrial origin by detecting helium and other substances incorporated in the sediments that could only be explained by the solar wind having bombarded the dust, enriching it with those elements on its way to Earth.

Our results clearly show that enormous amounts of fine-grained dust reached Earth shortly after the breakup. And the geological record shows that shortly after the dust arrived, the sea level fell dramatically worldwide – the beginning of the ice age. That was because the sea water was transferred to the high latitudes, where large ice sheets formed. ...

FULL STORY: https://www.sciencealert.com/asteroid-dust-may-have-triggered-an-ice-age-466-million-years-ago
 
See Also ...
Dust from a giant asteroid crash caused an ancient ice age
Date: September 18, 2019
Source: Field Museum

Summary: About 466 million years ago, long before the age of the dinosaurs, the Earth froze. The seas began to ice over at the Earth's poles, and new species evolved with the new temperatures. The cause of this ice age was a mystery, until now: a new study argues that the ice age was caused by global cooling, triggered by extra dust in the atmosphere from a giant asteroid collision in outer space.

FULL STORY: https://www.sciencedaily.com/releases/2019/09/190918142025.htm
 
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